A demand for an in-cylinder injection gasoline engine is expected to increase as fuel efficiency requirements are tightened for an internal combustion engine installed to a vehicle. However, an in-cylinder injection gasoline engine may possibly have a larger amount of PM (Particulate Matter) emission than an intake-port injection gasoline engine. In order to eliminate such a possibility, a filter capturing PM discharged from the engine is disposed in an exhaust passage of the engine.
A technique to diagnose an abnormality of the PM capturing filter is disclosed in, for example, Patent Literature 1 (JP2007-315275A). According to the disclosed technique, a PM sensor detecting an amount of PM in an exhaust gas is provided downstream of the PM capturing filter and presence or absence of a failure of the filter is determined depending on whether an amount of PM detected by the PM sensor exceeds a determination value under a condition that capturing efficiency of the filter is at or above a predetermined value.
A type of the PM capturing filter in the related art has a structure in which some of multiple cells provided to the filter are closed on an inlet side and the other cells (that is, inlet-opened cells) are closed on an outlet side.